Tandem cylinder disc brake

ABSTRACT

A tandem cylinder caliper disc brake is disclosed which includes a two-piece caliper housing. The main portion of the caliper includes a housing which defines the usual bore therewithin in which the actuating piston of the brake is adapted to reciprocate. The second portion of the caliper is a plug which is secured to the main portion by suitable fastening means and which cooperate with the wall of the bore to define an annular chamber therebetween. The actuating piston includes an annular section and a transversely extending section which closes one end of the annular section. The annular section is slidably received within the annular chamber defined between the plug and the walls of the bore. A first chamber defined between the end of the annular section and the corresponding end of the bore is communicated to a first vehicle hydraulic system, and a second chamber defined between the transversely extending portion of the piston and the end of the plug is communicated to a second vehicle hydraulic system. A pair of axially spaced seals carried by the plug engage the inner circumferential surface of the annular section of the piston. A pair of spaced static seals are disposed between the plug and the main portion of the caliper. Vents are provided to communicate the portion of the interface between the plug and the piston between the two dynamic seals and the portion of the interface between the plug and the main portion of the caliper between the two static seals to the exterior of the caliper.

United States Patent [191 Burnett [54] TANDEM CYLINDER DISC DRAKE [75]Inventor: Richard T. Burnett, South Bend,

3,477,549 11/1969 Barton 188/345 3,486,591 12/1969 Schefiier ..188/345 X3,576,236 4/1971 Laverdant 1 88/345 FOREIGN PATENTS OR APPLICATIONS424,193 A 2/ 1935 Great Britain ..60/5.4.6 M

Primary Examiner-GeorgeE. A. Halvosa Attorney-Ken C. Decker and Plante,Hartz, Smith Thompson 51 Apr. 3, 1973 57 ABSTRACT A tandem cylindercaliper disc brake is disclosed which includes a two-piece caliperhousing. The main portion of the caliper includes a housing whichdefines the usual bore therewithin in which the actuating piston of thebrake is adapted to reciprocate. The second portion of the caliper 'is aplug which is secured to the main portion by suitable fastening meansand which cooperate with the wall of the bore to define an annularchamber therebetween. The actuating piston includes an annular sectionand a transversely extending section which closes one end of the annularsection. The annular section is slidably received within the annularchamber defined between the plug and the walls of the bore. A firstchamber defined between the end of the annular section and thecorresponding end of the bore is communicated to a first vehiclehydraulic system, and a second chamber defined between the transverselyextending portion of the piston and the end of the plug is communicatedto a second vehicle hydraulicsystem. A pair of axially spaced sealscarried by'the plug engage the inner circumferential surface of theannular section of the piston. A pair of spaced static seals aredisposed between the plug and the main portion of the caliper. Vents areprovided to communicate the portion of the interfacebetween the plug andthe piston between the two dynamic seals and the portion of theinterface between the plug and the main portion of the caliper betweenthe two static seals to the exterior of the caliper.

2 Claims, 4 Drawing Figures ma /60a 1? B0 TANDEM CYLINDER'DISC BRAKEBACKGROUND OF THE INVENTION This invention relates to a tandem cylindercaliper disc brake.

It has been desirable and, more recently required by law, to have thebrake applying hydraulic system of an automotive vehicle divided intotwo or more sections so that a single failure, such as a hydraulic leak,will not render all of the vehicles brakes inoperative. This has usuallybeen done by having the front wheel brakes in one system and the rearwheel brakes in another system. However, recently published proposedfederal safety standards require that the vehicle be able to stop, uponfailure of one of the hydraulic systems, in a distance which cannot bemet by the rear brakes alone on many vehicles because of insufficientweight on the rear axle, which results in rear wheel slide. Therefore,it is necessary to have split front brakes in which at least a portionof each front brake can be used in conjunction with one or more rearbrakes. In some commercial vehicles, split rear brakes may be required.

Although brakes of this type have been proposed before, they haveusually been quite difficult to manufacture. For example, one designprovides a caliper housing which slidably receives an annular portion ofthe actuating piston in a rather narrow annular chamber within thecaliper. However, the annular chamber is so narrow that it is oftendifficult, if not impossible, to machine grooves in the walls of theannular chamber which support the necessary seals to prevent fluidcommunication from one hydraulic system to the other. Another difficultywith this design is that opposite sides of a single seal are exposed tofluid pressures from different hydraulic systems, so that a seal failurewould be undetected and would also permit communication of hydraulicfluid from one of the hydraulic systems to the other system, therebydefeating the purpose of splitting the systems.

SUMMARY OF THE INVENTION Therefore, an important object of thisinvention is to provide a tandem cylinder caliper disc brake which issubstantially easier to manufacture than similar disc brakes known inthe prior art.

Another important object of my invention is to prevent fluidcommunication between the two hydraulic systems used to actuate tandemcylinder disc brakes even if one of the seals which engage the pistonfails.

Another important object of my invention is to provide a tandem cylinderdisc brake having a pair of axially spaced dynamic seals which slidablyengage the piston, and to vent the interface between the piston and thecaliper between the spaced dynamic seals to the exterior of the vehicle,to thereby prevent fluid communication between the two' hydraulicactuating systems even if one ofthe seals fail.

A still further object of my invention is to provide a tandem cylinderdisc brakehaving a two-piece caliper including a main body portiondefining a chamber therewithin and a plug which is installed in thechamber aftersuitable seal receiving grooves are machined on the plug.

A still further important object of my invention is to provide a tandemcylinder disc brake having a pair of spaced static seals between theplug and the main body portion of the caliper and to vent the interfacebetween the plug and the main portion of the caliper between the staticseal to the exterior of the brake.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a tandemcylinder caliper disc brake made pursuant to the teachings of.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG.1, a disc brake generally indicated by the numeral 10 includes a rotor12 having a pair of friction faces 14 and 16. A pair of frictionelements 18, 20 are disposed adjacent corresponding friction faces 14and 16 respectively, and are adapted to be urged into braking engagementwith the latter by a caliper generally indicated by the numeral Thecaliper 22 includes a main body housing 24 defines a bore 26 therewithinwhich is disposed adjacent the friction element 18. Caliper 22 furtherincludes a bridge portion 28 which extends across the periphery of therotor 12 and an inwardly extending portion 30 which is adapted to engagethe friction element 20. A torque member 32 is: rigidly secured to aportion of the vehicle and slidably supports the caliper 22 which may beconnected to the torque member3l2 by any well-known method, such as theone disclpsed U. S. Pat. No. 3,388,774 owned by the assignee of presentinvention and incorporated herein by reference. I

Caliper 22 further includes a plug 34 which is releasably secured in thebore 26 by an appropriate fastening means, such as by the bolt 36. Theplug 34 is counterbored as at 38 to receive the head of the bolt 36. Thethreaded end of the bolt 36 engages corresponding threads provided in acounterbore in the housing 24. The outer circumferential surface of theplug 34 cooperates with the wall of the bore 26 to define an annularchamber therebetween, which slidably receives an annular section 42 ofan actuating piston generally indicated by the numeral. Piston furtherincludes a transversely extending section 46 which closes one end of theannular section 42 The outer side of the transversely extending sectionof piston 44 is adapted to engage the friction element .18 for urgingthe latter toward the friction face 14 whena brake application iseffected. The inner side of ,the transversely extending section 46cooperates ,with the end of the plug 34 to define avariable-volumechamber 48 therebetween. The chamber 48 is communicatedwith one of the vehicles hydraulic brake actuating systems by passagemeans which includes a passage s o extending through the bolt 36, thecounterbore and another passage 52 which communicates the counterbore 40with an inlet port on the exterior. of the c aliper .22. Similarly, theend of the annular ,section 42 cooperates with the end of the bore 26 todefine another variablelvolume chamber 54. The chamber 54 iscommunicated to a second vehicle hydraulic brake actuating system by apassage 56. Suitable bleed passages 58 and 59 within the housing and theplug, respectively, permit egress of air from the chamber 48 when thelatter is initially charged with fluid. A suitable device such as rollpin 61 orients the plug 34 so that the bleed passage 59 communicateswith the passage 58.

A static seal 60 is carried by the plug 34 for sealing engagement withthe housing 24 to prevent fluid communication through the interfacebetween the plug and the housing. A boot 62 is also provided to preventcontaminants from the exterior of the brake from damaging the wall ofthe bore 26. The outer circumferential surface of the plug 34 isprovided with a groove 64 which receives a suitable dynamic seal 66which slidingly and sealingly engages the inner circumferential surfaceof the annular section 42 of piston 44. Similarly, the wall of the bore26 is provided with a circumferentially extending groove 68 whichsupports a seal 70 which slidingly and sealingly engages the outercircumferential surface of the annular section 42. In prior art discbrakes, it was often difficult if not impossible to machine the wall ofthe bore 26, the outer circumferential surface of the membercorresponding to plug 34, and to machine the grooves 68 and 64 in theirproper places, because the width of the annular chamber which receivesthe annular section of piston 42 was so smalLHowever, in the presentdevice, an appropriate tool may be inserted into the bore 26 from theopen end of the latter to machine the walls of the boreQSimilarly, thegroove 68 may be cut in the bore 26 before the plug 34 is installed. Theouter circumferential surface of the plug 34 may be machined and thegroove 64 cut in the latter before the plug 34 is installed within thehousing 24. As can be seen by those skilled in the art, by providing atwo-piece caliper consisting of the main housing 24 and the plug 34,machining and assembly of the caliper 22 is considerably simplified.

In operation, when the vehicle operator depresses the brake pedal,thereby developing pressure in the vehicles master cylinder (not shown),fluid pressure is delivered from the master cylinder to the chamber 48through a first hydraulic system and from the master cylinder to thechamber 54 through a second hydraulic system. Fluid pressure in thechambers 48 and 54 urge the pistons 44 to the right viewing FIG. 1thereby urging the friction element 18 into braking engagement with thefriction face 14. Since the caliper 22 is slidably mounted on the torquemember 32, reaction forces acting through the bridge portion 28 and theinwardly extending portion 30 also urge the friction element 20 intoengagement with the friction face 16. Should one of the vehicleshydraulic systems fail, thereby failing to pressurize one of thechambers 54 or 48, sufficient pressure will be developed to actuate thebrake.

DETAILED DESCRIPTION OF THE FIRST AND SECOND ALTERNATE EMBODIMENTS Inthe first alternate embodiment illustrated in FIG. 2, elements the sameor substantially the same as those in the preferred embodiment retainthe same reference numerals, but are preceded by the numeral 1.Similarly,

in the second alternate embodiment illustrated in FIG. 3, elementssubstantially the same as those in the preferred embodiment retain thesame reference character, but are preceded by the numeral 2. As will beappreciated by those skilled in the art, opposite sides of the dynamicseal 66 in FIG. 1 are exposed to pressures in the chambers 54 and 48,respectively. There,- fore, if the seal 66 should fail, fluid pressurein one of the chambers 54 or 48 will be communicated to the otherchamber and into the other vehicle hydraulic system, thus defeating thepurpose of providing a split system brake in that a failure in one ofthe hydraulic systems would also cause a failure in the other hydraulicsystem. Similarly, opposite sides of the static seal 60 in FIG. lareexposed to pressure of different hydraulic systems so that, if the seal60 should fail, fluid from one of the systems would also be communicatedto the other system. However, in the embodiment of FIG. 2, the singleseal 66 of the FIG. 1 embodiment is replaced by a pair of axially spacedseals 166a and 166b, each of which sealingly and slidingly engage theinner circumferential surface of the piston 144. Similarly, the staticseal 6 of the embodiment of FIG. 1 is replaced by a pair of seals a and16%. That portion of the interface between the plug 134- and the housing124 between seals 160a and l60b is communicated to the exterior of thebrake housing by a vent passage 172 which extends through the housing24. Similarly, that portion of the interface between the outercircumferential surface of the plug 134 and the inner circumferentialsurface of the annular section 142 of piston 144 between the seals 166aand 166b is also vented to the exterior of the brake through a ventpassage 174 and the vent passage 172. Therefore, if one of the seals166a or 166b should fail, fluid from the corresponding hydraulic systemleaking past the failed seal will be communicated to the exterior of thevehicle while the other hydraulic system remains sealed by the otherseal. Upon failure of one of the seals 160a or 160b, fluid pressure fromthe corresponding system will also be communicated to the exterior ofthe vehicle, leaving the other seal, and therefore, the other hydraulicsystem, operable. The embodiment of FIG. 3 is essentially the same asthe embodiment of FIG. 2, except that the seals 266a and 266b arecarried in grooves 264a and 2641; provided in the piston 244 instead ofin the plug 234. The appropriate vent 274 which communicates the portionof the interface between the plug and the piston extending between theseals 266a and 266b is formed within the piston 244 instead of withinthe plug 234. A second passage 272 is also provided which communicatesthe interface between the plug 234 and housing 224 extending between theseals 260a and 260b to the exterior of the vehicle.

DETAILED DESCRIPTION OF THE THIRD ALTERNATE EMBODIMENT In the embodimentof FIG. 4, elements substantially the same as those in the embodiment ofFIG. I retain the same reference character, but are preceded by thenumeral 3. In the embodiment of FIG. 4, the bore 326 is stepped toprevent larger and smaller diameter sections 376 and 378, respectively,with a shoulder 380 therebetween. A stepped piston 382 has larger andsmaller diameter portions slidably received in the larger and smallerdiameter portions of the bore respectively, which present a shoulder 384therebetween. An automatic adjuster generally indicated by the referencenumeral 386 interconnects the pistons 382 and 344. The automaticadjuster may be of the type more completely disclosed in U. S. patentapplication Ser. No. 863,482, filed Oct. 3, 1969, owned by the assigneeof the present invention and incorporated herein by reference. Thesmaller diameter end of the piston 382 cooperates with the end of thebore 326 to define a first variable volume chamber 388 therebetweenwhich is communicated with one of the vehicles brake hydraulic systemsby a passage 390. The variable-volume chamber 389 defined between thepistons 382 and 344 is communicated to the other brake hydraulic systemby the passage 392. First and second axially spaced dynamic seals 394and 396 slidingly and sealingly engage the smaller and larger diameterportions of the piston 382 respectively. A vent passage 398 communicatesthe chamber defined between the shoulders 380 and 384 to the exterior ofthe vehicle. In operation, when a brake application is effected withboth of the vehicle brake hydraulic systems operative, fluid pressuredeveloped in the master cylinder will be communicated into the chambers388 and 389 respectively. However, since the fluid pressure in chamber389 acts across the larger face of the piston 382, the latter willremain in its rearwardmost position while the piston 344 is urged to theright viewing FIG. 4, thereby effecting a brake application in thenormal manner. If the movement required of piston 344 to actuate thevehilcles brakes exceeds the predetermined amount, the automaticadjuster 386 limits retraction of the piston when the brake is releasedto the predetermined amount, thereby maintaining the proper clearancebetween the friction elements and their corresponding friction faces. Ifthe hydraulic system communicated to the chamber 389 should leak, fluidpressure in the chamber 388 will be sufficient to actuate the brake.Similarly, if the vehicle hydraulic brake system communicated to thechamber 388 should leak, pressure in chamber 389 will actuate the brakein the normal manner. If one of the seals 394 or 396 should fail,pressure from the effected chamber 388 or 389 leaking past thecorresponding seal will be communicated to exterior of the brake throughthe vent passage 398, thereby permitting the other seal to maintainpressure in the other chamber for actuating the brake.

Iclaim:

I. In a disc brake:

a rotor having a pair of friction faces;

a pair of friction elements, one of said elements being disposedadjacent each of said friction faces;

a torque member;

a caliper slidably mounted on said torque member straddling said rotorand operatively connected to each of said friction elements for urgingthe latter into braking engagement with their corresponding frictionfaces when a brake application is effected;

said caliper including a housing defining a bore therewithin and furtherincluding a plug within said bore, the outer circumferential surface ofsaid plug cooperating with the wall of the bore to define an annularchamber therebetween, fasten- 1ng means releasably securing said plug tosaid caliper, and a piston slidably mounted within said bore, saidpiston including an annular section and a transversely extending sectionclosing one end of the annular section, said annular section beingreceived within said annular chamber and slidingly and sealinglyengaging the wall of the bore and the outer circumferential surface ofthe plug;

said annular portion of the piston cooperating with the end of the boreto define a first variablevolume chamber therebetween, said firstchamber being communicated to a first fluid pressure source;

said transversely extending portion of said piston cooperating with theend of said plug to define a second variable-volume chambertherebetween, said second chamber being communicated to a second fluidpressure source;

a pair of spaced dynamic seals to prevent fluid communication betweensaid first and second chambers through the interface between theplug'and the piston; i

a pair of spaced static seals disposed between the plug and the housingto prevent fluid communication through the interface between the plugand the housing; 1

a first fluid passage extending through said plug and communicating thatportion of the interface between the piston and the plug intermediatethe dynamic seals to that portion of the interface between said plug andthe housing intermediate the static seals, and second passage meanscommunicating that portion of the interface between the plug and thehousing intermediate said static seals to the exterior of said housing;and

detent means orienting said plug circumferentially with respect to thehousing to thereby align first passage means with said second passagemeans.

2. The invention of claim 1:

said detent means including a pin carried .by said housing and arecessin said-plug receiving the pin when the plug is installed upon thehousing. 2

1. In a disc brake: a rotor having a pair of friction faces; a pair offriction elements, one of said elements being disposed adjacent each ofsaid friction faces; a torque member; a caliper slidably mounted on saidtorque member straddling said rotor and operatively connected to each ofsaid friction elements for urging the latter into braking engagementwith their corresponding friction faces when a brake application iseffected; said caliper including a housing defining a bore therewithinand further including a plug within said bore, the outer circumferentialsurface of said plug cooperating with the wall of the bore to define anannular chamber therebetween, fastening means releasably securing saidplug to said caliper, and a piston slidably mounted within said bore,said piston including an annular section and a transversely extendingsection closing one end of the annular section, said annular sectionbeing received within said annular chamber and slidingly and sealinglyengaging the wall of the bore and the outer circumferential surface ofthe plug; said annular portion of the piston cooperating with the end ofthe bore to define a first variable-volume chamber therebetween, saidfirst chamber being communicated to a first fluid pressure source; saidtransversely extending portion of said piston cooperating with the endof said plug to define a second variable-volume chamber therebetween,said second chamber being communicated to a second fluid pressuresource; a pair of spaced dynamic seals to prevent fluid communicationbetween said first and second chambers through the interface between theplug and the piston; a pair of spaced static seals disposed between theplug and the housing to prevent fluid communication through theinterface between the plug and the housing; a first fluid passageextending through said plug and communicating that portion of theinterface between the piston and the plug intermediate the dynamic sealsto that portion of the interface between said plug and the housingintermediate the static seals, and second passage means communicatingthat portion of the interface between tHe plug and the housingintermediate said static seals to the exterior of said housing; anddetent means orienting said plug circumferentially with respect to thehousing to thereby align first passage means with said second passagemeans.
 2. The invention of claim 1: said detent means including a pincarried by said housing and a recess in said plug receiving the pin whenthe plug is installed upon the housing.